where can i use php?

i mean,can i put normal php codes into this framework to achive some functions?  if so,where in this framework can i write the php code?

in other word, any php code can all be used in this framework? where to use? 

It depends on what you're trying to do. I'm only just starting out myself but I would think that most modifications would be done by adding new methods/functions into the model files.

What is it your trying to do?

I want to achive the fonctions like bbs,blog, cms,leave message ,img upload ,mail system and so on,

can this framework support those?

Of course. But first you have to RTFM, like this one.